Fine coal and coal tending to burst upon subjection to heavy thermal loads cannot be used effectively as a carbon carrying reduction agent in a process in which pig iron is produced from iron ore wherein a fluidized bed is formed in a melt-down gasifier. Pre-treatment of lumpy coal tending to burst or of fine coal by one of the two methods described herein, however, permits the effective employment of most grades of coal and of fine coal as lumpy carbon carriers.
To produce pig iron from iron ore, the ore is first pre-reduced in at least one reduction step to form sponge iron. The sponge iron is then transported into a melt-down gasifier. To aid the subsequent final reducing and melting of the sponge iron, a lumpy carbon carrying reduction agent is introduced into the upper portion of the gasifier to form, together with the sponge iron, a fluidized bed and a solid bed of carbon carrier underneath the fluidized bed.
This reduction agent consists preferably of coal, in particular long-flame gas coal with a grain size of up to 50 mm, which has been dried degassed and subsequently converted into coke in the upper area of the melt-down gasifier. Therefore, a fluidized bed of coke is produced in the melt-down gasifier.
The formation of an optimum fluidized bed required for the melting and final reducing, and of a solid bed forming underneath the fluidized bed depends on the grain distribution of the coke particles produced in the meltdown gasifier. Many grades of coal tend to burst more or less violently when being fed into the head area of the gasifier due to the shock-like thermal load they are subjected to when brought into the there prevailing temperature of approximately 1,000.degree. C., alterating the grain distribution accordingly.
Alternatively, the available coal may not have a sufficient grain size. The production of fine coal having a grain size of less than 1 mm constitutes approximately 30% of all coal produced by underground mining and this percentage is expected to increase further due to mining methods and preparation plants. Such fine coals, as well as coarse-grain coals tending to burst easily, are therefore less suitable for use in a melt-down gasifier working with a fluidized bed.
It is therefore the object of the present invention to provide a method for pretreating coals tending to burst or fine coals so as to form a lumpy carbon carrier suitable for the formation of a fluidized bed and a solid bed in a melt-down gasifier. The lumpy carbon carrier thus formed is used in a production of pig iron from iron ore wherein the ore is prereduced in one or in a plurality of reduction plants to iron sponge, and the iron sponge is subsequently fused and finally reduced in the melt-down gasifier with the help of the lumpy carbon carrier and an oxygen-containing gas. The lumpy carbon carrier is fed into the upper part of the melt-down gasifier and the oxygen-containing gas if fed into the lower part of the melt-down gasifier forming within the melt-down gasifier a fluidized bed with a solid bed of the lumpy carbon carrier being formed underneath the fluidized bed.